Well, what I usually do does not depend on the type of plate I use. Typically SH-SY5Y detach easily when die, and I do not think it is something you can change. Try to count the surviving cells with your system, and refering survival population to the one in the control group. That is the typical approach.

If you are still interested in the number of dead cells you could try to centrifugate the medium you are removing- that contains the floating cells- and using the pellet somehow in your essay. However, I have no experience doing this.

I have experience measuring late-apoptotic SH-SY5Y cells (I use propidium iodide staining), and I definitely recall having experience with floating cells being inadvertently discarded during media changes. Xabier is right - I found a solution to this by centrifuging my 96-well plates and then performing the stain. I found I got a much more reliable and accurate result. As for plating, there shouldn't be an issue with using any muti-well plate you desire, depending on the sort of cell number you're hoping to extract data from. The problem of cell loss will likely occur no matter which plate you use, and likewise, centrifuging should hopefully be a useful remedy to each of them.

Hope that helps